To avoid severe optical aberrations in his long instruments, how did Galileo manage the focal length in relation to the aperture?

Answer

The focal length of the objective lens had to be relatively long

Shorter focal lengths introduced severe aberrations; therefore, Galileo constructed instruments with focal lengths reaching several feet to achieve the best possible view given the lens technology of his era.

To avoid severe optical aberrations in his long instruments, how did Galileo manage the focal length in relation to the aperture?
Galileo GalileitelescopeAstronomerinstrumentOptic